The present invention relates to a device for determining rotary motions and for generating an electric alternating signal representative of the rotary motion, including a signal generator which undergoes the rotary motion and, in the form of a ring, wheel, hollow cylinder, or a similar element, is provided with inwardly directed teeth or projections, and a stationary, inductive transducer which is arranged within the surface of the signal generator and is designed as a double-sided measuring coil that comprises a core of permanent magnets and elongated pole shoes which project from either side of the measuring coil up to the signal generator, wherein the inwardly directed teeth or projections and the pole shoes are designed, arranged and conformed to each other so that, whenever an end piece of a pole shoe points to a tooth or a projection, the second, diametrically opposite end piece of the pole shoe faces a tooth gap or depression.
German patent application No. 42 13 977 discloses a device of this type. In this device, a double-sided measuring coil is arranged in a signal generator ring with inwardly directed teeth. The measuring coil has a core made of a permanent magnet magnetized perpendicularly to the axis of the measuring coil. Mounted on the pole surfaces of the permanent magnet, i.e. between the core and coil, is one elongated pole shoe which projects from either side of the coil and reaches up to the inwardly directed teeth. The pole shoes and the inwardly directed teeth are offset from each other, or rather conformed to each other so that whenever a pole shoe end points to a tooth, the diametrically opposite pole shoe end points to a tooth gap.
Further, a rotational speed measuring device is disclosed in German patent application No. 39 27 007 which also has a toothed disc with inwardly directed teeth as a signal generator. Inside the signal generator, there is a diametrically aligned measuring coil. The coil encloses a magnetic flux guide piece the length of which approximately corresponds to the inside diameter, reduced by the necessary distance to allow an air gap between the ends of the flux guide piece and the teeth of the signal generator. The flux guide piece protrudes from both sides of the coil. Permanent magnets, oriented such that they are magnetized perpendicularly to the magnetic flux guide piece, are placed on the ends of the flux guide piece. If there are signal generator teeth opposite the two magnets of a coil side, a magnetic flux forms from the respective outside of the magnets through the toothed disc to the flux guide piece and then to the inside of the magnets. When the tooth gaps are opposite the two magnets, the main flux passes through the air gap to the flux guide piece and the insides of the magnets. Thus, on the two coil sides the magnetic flux is alternating through the magnetic flux guide piece depending on whether tooth gaps or teeth are opposite the magnets.